Synthetic antiferromagnetic structure for magnetoelectronic devices

ABSTRACT

A nearly balanced synthetic antiferromagnetic (SAF) structure that can be advantageously used in magnetoelectronic devices such as a magnetoresistive memory cell includes two ferromagnetic layers and an antiferromagnetic coupling layer separating the two ferromagnetic layers. The SAF free layer has weakly coupled regions formed in the antiferromagnetic coupling layer by a treatment such as annealing, layering of the antiferromagnetic coupling layer, or forming the antiferromagnetic coupling layer over a roughened surface of a ferromagnetic layer. The weakly coupled regions lower the flop field of the SAF free layer in comparison to untreated SAF free layers. The SAF flop is used during the write operation of such a structure and its reduction results in lower power consumption during write operations and correspondingly increased device performance.

RELATED APPLICATION

[0001] This application is related to a co-pending application entitled“A Method Of Writing To A Scalable Magnetoresistance Random Access ToMemory Element” U.S. Ser. No. 09/978859 filed on Oct. 16, 2001, assignedto the assignee of the instant application.

FIELD OF THE INVENTION

[0002] This invention relates to semiconductor magnetoeletronic devices,and in particular, the present invention relates to semiconductorstructures useful in devices that store a magnetic state.

BACKGROUND OF THE INVENTION

[0003] The class of devices that is magnetoelectronic devices is a broadclass that includes motors, disk drives, and certain semiconductormemory devices, such as magnetoresistive random access memories (MRAMs),and integrated circuits that include MRAM and logic functions other thanMRAM, such as radio and processing circuits. Memory devices of all typesare an extremely important component in electronic systems. The threemost prevalent semiconductor memory technologies are SRAM (static randomaccess memory), DRAM (dynamic random access memory), and FLASH (a formof non-volatile random access memory), which are essentiallynon-magnetoelectronic. Each of these memory devices uses an electroniccharge to store information and each has its own advantages. SRAM hasfast read and write speeds, but it is volatile and requires large cellarea. DRAM has high density, but it is also volatile and requires arefresh of the storage capacitor every few milliseconds. Thisrequirement increases the complexity of the control electronics.

[0004] FLASH is the major nonvolatile memory device in use today. FLASHuses charge trapped in a floating oxide layer to store information.Drawbacks to FLASH include high voltage requirements and slow programand erase times. Also, FLASH memory has a poor write endurance of 10⁴-10⁶ cycles before memory failure. In addition, to maintain reasonable dataretention, the thickness of the gate oxide has to stay above thethreshold that allows electron tunneling, thus restricting FLASH'sscaling trends.

[0005] To overcome these shortcomings, new magnetic memory devices arebeing evaluated. One such device is the MRAM, which stores bits asmagnetic states. MRAM has the potential to have speed performancesimilar to DRAM. To be commercially viable, however, MRAM must havecomparable memory density to current memory technologies, be scalablefor future generations, operate at low voltages, have low powerconsumption, and have competitive read/write speeds.

[0006] A significant amount of power is consumed during a writeoperation of an MRAM cell in an MRAM device having an array of cells.The write operation consists of passing currents through conductivelines external but in close proximity to the MRAM magnetic element. Themagnetic fields generated by these currents are sufficient to switch themagnetic state of the free layer of the magnetic element. In addition,as the bit dimension shrinks, the switching field increases for a givenshape and film thickness, requiring more current to switch. As will bediscussed in more detail below, data is stored in the magnetizationstate of the free layer of the magnetic element. Therefore a significantchallenge to commercializing MRAM devices is to construct MRAM cellsthat switch the magnetic state using the lowest possible magnetic field,resulting in the lowest possible write currents, while maintaining theintegrity of the data within the entire array of elements

[0007] It would be highly advantageous, therefore, to remedy theforegoing and other deficiencies inherent in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention is illustrated by way of example and notlimitation in the accompanying figures, in which like referencesindicate similar elements, and in which:

[0009]FIG. 1 is a simplified cross-sectional view of a magnetoresistiverandom access memory (MRAM) device, in accordance with the presentinvention;

[0010]FIG. 2 is a simplified cross-sectional view of an MRAM device, inaccordance with embodiments of the present invention that use aSavtchenko writing technique;

[0011]FIG. 3 is a simplified plan view of part of the MRAM devicedescribed with reference to FIG. 2, showing word and digit lines;

[0012]FIG. 4 is a graph showing results of a simulation of the magneticfield amplitude combinations that produce the direct or toggle writemode in the MRAM device described with reference to FIG. 2;

[0013]FIG. 5 is a timing graph showing the word current and the digitcurrent of the MRAM device described with reference to FIG. 2;

[0014]FIG. 6 is a vector diagram showing the rotation of the magneticmoments for a magnetoresistive random access memory device for thetoggle write mode when writing a ‘1’ to a ‘0 in the MRAM devicedescribed with reference to FIG. 2;

[0015]FIG. 7 is a vector diagram showing the rotation of the magneticmoments for a magnetoresistive random access memory device for thetoggle write mode when writing a ‘0’ to a ‘1’ in the MRAM devicedescribed with reference to FIG. 2;

[0016]FIG. 8 is a vector diagram showing the rotation of the magneticmoments for a magnetoresistive random access memory device for thedirect write mode when writing a ‘1’ to a ‘0’ in the MRAM devicedescribed with reference to FIG. 2;

[0017]FIG. 9 is a vector diagram showing the rotation of the magneticmoments for a magnetoresistive random access memory device for thedirect write mode when writing a ‘0’ to a state that is already a ‘0’ inthe MRAM device described with reference to FIG. 2;

[0018]FIG. 10 is a timing graph of the word current and the digitcurrent when only the digit current is turned on in the MRAM devicedescribed with reference to FIG. 2;

[0019]FIG. 11 is a vector diagram showing the rotation of the magneticmoments for a magnetoresistive random access memory device when only thedigit current is turned on in the MRAM device described with referenceto FIG. 2;

[0020]FIG. 12 is a graph that shows plots of a normalized magneticmoment versus an applied field for two samples of nearly balancedsynthetic antiferromagnetic structures;

[0021]FIG. 13 is an enlarged view of the center portion of FIG. 12;

[0022]FIG. 14 is a perspective drawing of a portion of a syntheticantiferromagnetic structure fabricated in accordance with the presentinvention;

[0023]FIGS. 15 and 16 are flow charts of processes for fabricating amagnetoresistive tunneling junction memory cell in accordance withembodiments of the present invention.

[0024] Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0025] Referring to FIG. 1, a simplified cross-sectional view of ageneralized MRAM array 3 is shown, in accordance with the presentinvention. In this illustration, only a single magnetoresistive memorydevice (or cell) 10 is shown, but it will be understood that MRAM array3 consists of a number of MRAM devices 10 and only one such device isshown for simplicity in describing a reading method.

[0026] MRAM device 10 is a magnetoresistive tunneling junction memorycell, or magnetoresistive tunneling junction device (MTJD) thatcomprises material layers sandwiched between writing conductors that area word line 20 and a digit line 30. Word line 20 and digit line 30include conductive material through which a current can be passed toinduce a magnetic field within the MRAM device 10. In this illustration,word line 20 is positioned on top of MRAM device 10 and digit line 30 ispositioned on the bottom of MRAM device 10 and is directed at a 90°angle to word line 20 (See FIG. 3). It will be appreciated thatconductors such as word line 20 and digit line 30 need not be inphysical contact with the other layers of the MRAM device 10 forefficient reading and writing operation, the conductors just need to besufficiently near the regions to which the magnetic field is to beapplied such that the magnetic field is effective.

[0027] MRAM device 10 includes a bit magnetic region 15, a referencemagnetic region 17, and an electrically insulating material that forms alayer that acts as a tunneling barrier 16, as well as those portions ofthe word line 20 and digit line 30 that carry currents that affect theoperation of the MRAM device 10. The bit magnetic region 15 andreference magnetic region 17 may each comprise more than one layer, someof which can have a magnetic moment (all magnetic moments arerepresented herein as vectors) associated therewith. For example, someconventional MRAMs have a bit magnetic region 15 that is a singleferromagnetic layer or a multilayered unbalanced syntheticantiferromagnetic region. Bit magnetic region 15 for the presentinvention is a nearly balanced multilayer synthetic antiferromagnetic asdescribed below. The bit magnetic region 15 and reference magneticregion 17 are positioned adjacent to the tunneling barrier 16, onopposite sides thereof. A resistance of the MTJD is determined by therelative polarization directions of a bit magnetic moment and areference magnetic moment directly in contact with the tunnel barrier.The magnetic moment is a physical property of ferromagnetic materials.The magnetic material and the relative angle of polarization of region15 or 17 directly adjacent to the tunnel barrier determine the high orlow state. In the embodiments described herein, the bit magnetic regionis a free ferromagnetic region, meaning that the bit magnetic moment isfree to rotate in the presence of an applied magnetic field. The bitmagnetic moment has two stable polarities (states) in the absence of anyapplied magnetic fields along a magnetic axis, known herein as the “biteasy axis”, determined at the time of deposition of the magneticmaterial and fabrication of the magnetic regions 15 of the MRAM array 3.An axis orthogonal to the bit easy axis is known as the “hard axis”.

[0028] Referring to FIG. 2, a cross sectional view of a portion of anMRAM array 5 that includes an MRAM device 72 is shown, in accordancewith embodiments of the present invention, which uses a Savtchenkowriting technique described herein in some detail with reference toFIGS. 2-11. MRAM device 72 has the structure described with reference toFIG. 1, with a refined description that the bit magnetic region 15comprises at least three layers and has magnetic moments implemented aswith reference to FIGS. 2-11. Bit magnetic region 15 in this example isa tri-layer structure, which has an antiparallel coupling layer 65sandwiched between two ferromagnetic layers 45 and 55, providing what isknown as a synthetic antiferromagnetic (hereinafter referred to as“SAF”) layer. The nominal thicknesses 42, 51 of the ferromagnetic layers45, 55 are in a range from 5 to 150 Angstroms, and the nominal thickness46 of the antiparallel coupling layer 65 is in a range from 3 to 30Angstroms. “Nominal” in this context means an approximate, averagethickness within normal manufacturing tolerances for the type ofmaterial and process used to deposit it.

[0029] Ferromagnetic layers 45, 55 have magnetic moments 58 and 53 (seeFIG. 3), respectively, that have respective vector values M₁ and M₂.Further, ferromagnetic layers 45, 55 include at least one of elementsNi, Fe, Co, Mn or combinations thereof. Antiparallel coupling layer 65includes a material that induces antiferromagnetic exchange coupling(also called herein an antiferromagnetic exchange material) between theferromagnetic layers 45, 55 or a material that prevents exchangecoupling (also called herein a spacing material) between theferromagnetic layers 45, 55, or both. The antiferromagnetic exchangematerial comprises one of the elements Ru, Os, Re, Cr, Rh, Cu, Nb, Mo,W, Ir, V, or combinations thereof, and is not by itself anantiferromagnetic material; rather it is a coupling layer that is key tocreating the antiferromagnetic-like properties of the SAF layer. Thespacing material is an insulator, of which one example is Al₂O₃, or aconductor, of which some examples are Ta and Al. The antiparallelcoupling layer 65 can comprise two or more layers, each of which may beantiferromagnetic exchange or spacing layers. The magnetic moments 58,53 are usually oriented anti-parallel due to the coupling of theantiparallel coupling layer 65. The coupling can be induced as when anantiferromagnetic exchange material is used as the antiparallel couplinglayer 65. or antiparallel coupling can also be generated by themagnetostatic fields of the ferromagnetic layers in the MRAM device 72.Therefore, the antiparallel coupling layer 65 need not necessarilyprovide any additional coupling beyond substantially eliminating theferromagnetic coupling between the two ferromagnetic layers 45, 55 andcould therefore be a spacing material, for example, an insulator such asAlO or a conductor such as Ta or Al. For the purposes of explaining theSavtchenko writing technique, there is also defined a net magneticmoment 40 that is the vector resultant of the magnetic moments 58 and53. Also, it will be understood that bit magnetic region 15 can includesynthetic antiferromagnetic layer material structures other thantri-layer structures and the use of tri-layer structures in thisembodiment is for illustrative purposes only. For example, one suchsynthetic antiferromagnetic layer material structure could include afive-layer stack of a ferromagnetic layer/antiparallel couplinglayer/ferromagnetic layer/antiparallel coupling layer/ferromagneticlayer structure. The number of ferromagnetic layers is identified as N.To simplify the description, it is assumed hereinafter that N is equalto two so that MRAM device 72 includes one tri-layer structure in bitmagnetic region 15 with magnetic moments 53 and 58, as well as a netmagnetic moment 40. Also, only the magnetic moments of bit magneticregion 15 are illustrated.

[0030] The magnetic moments 58, 53 in the two ferromagnetic layers 45,55 in the MRAM device 72 can have different thicknesses or material toprovide a net magnetic moment 40 given by ΔM=(M₂-M₁). In this case ofSavtchenko writing technology, this tri-layer structure will be nearlybalanced; that is, ΔM is less than 15 percent of the average of M₂ andM₁ (otherwise simply stated as “the imbalance is less than 15 percent”)and is preferably as near to zero as can be economically fabricated inproduction lots. The magnetic moments of the tri-layer structure of thebit magnetic region 15 are free to rotate with an applied magneticfield. In zero field the bit magnetic moment 58, which is the magneticmoment that is adjacent to the tunneling barrier 16, will be stable inone of two polarized directions along the easy axis.

[0031] A measurement current through the MRAM device 72 that is used toread the polarity of the bit magnetic moment 58 depends on the tunnelingmagnetoresistance, which is governed by the orientation and magnitudesof the bit magnetic moment 58 and a reference magnetic moment of thereference magnetic region 17. When these two magnetic moments areparallel, then the MRAM device resistance is low and a voltage bias willinduce a larger measurement current through the MRAM device 72. Thisstate is defined as a “1”. When these two magnetic moments areanti-parallel, then the MRAM device resistance is high and an appliedvoltage bias will induce a smaller measurement current through thedevice. This state is defined as a “0”. It will be understood that thesedefinitions are arbitrary and could be reversed, but are used in thisexample for illustrative purposes. Thus, in magnetoresistive memory,data storage is accomplished by applying magnetic fields that cause themagnetic moments in region 15 to be orientated either one of paralleland anti-parallel directions along the bit easy axis 59 relative toregion 17, and reading the written state relies upon resistancemeasurements that depend on the polarity of the bit magnetic momentrelative to the reference magnetic moment (This same operation is truefor all of the MRAM devices described herein)

[0032] The method of writing to the MRAM device 72 relies on thephenomenon of “spin-flop” for a nearly balanced SAF tri-layer structure,which is well known to one of ordinary skill in the art. Here, the term“nearly balanced” is defined such that the M1 and M2 are within 15% ofone another, and includes the case in which M1 and M2 are essentiallyequal. The “spin-flop” phenomenon lowers the total magnetic energy in anapplied field by rotating the magnetic moments of the ferromagneticlayers so that they are nominally orthogonal to the applied fielddirection but still predominantly anti-parallel to one another. Therotation, or “flop”, combined with a small deflection of eachferromagnetic magnetic moment in the direction of the applied fieldaccounts for the decrease in total magnetic energy.

[0033] MRAM device 72 preferably has tri-layer structure that has anon-circular shape characterized by a length/width ratio in a range of 1to 5. It will be understood that the bit magnetic region 15 of MRAMdevice 72 can have other shapes, such as square, elliptical,rectangular, or diamond, but it is illustrated as being circular forsimplicity.

[0034] Further, during fabrication of MRAM array 5, each succeedinglayer (i.e. 30, 55, 65, etc.) is deposited or otherwise formed insequence and each MRAM device 72 may be defined by selective deposition,photolithography processing, etching, etc. in any of the techniquesknown in the semiconductor industry. During deposition of at least theferromagnetic layers 45 and 55, a magnetic field is provided to set thebit easy axis. The provided magnetic field creates a preferredanisotropy axis for magnetic moments 53 and 58. The bit easy axis 59 ischosen to be at a 45° angle between word line 20 and digit line 30. Itwill be appreciated however that angles other than 45° could be used.

[0035] Referring to FIG. 3, a simplified plan view of parts of the MRAMarray 5 is shown, in accordance with embodiments of the presentinvention. Bit magnetic region 15 is shown as having an essentiallycircular shape in the MRAM device 72 of FIG. 2, but may alternativelyhave another shape, such as an ellipse, that has an aspect ratiosubstantially greater than 1. Bit magnetic moment 40 is oriented alongan anisotropic bit easy axis 59 in a direction that is essentially 45degrees to a writing conductor that is, in this example, the word line20. Another writing conductor, the data line 30, is orthogonal to theword line 20. To simplify the description of MRAM device 72, alldirections will be referenced to an x- and y-coordinate system 100 asshown and to a clockwise rotation direction 94 and a counter-clockwiserotation direction 96. In MRAM array 5, a word current 60 is defined asbeing positive if flowing in a positive x-direction and a digit current70 is defined as being positive if flowing in a positive y-direction.The purpose of word line 20 and digit line 30 is to create an appliedmagnetic field within MRAM device 10. A positive word current 60 willinduce a circumferential word magnetic field, H, 80, and a positivedigit current 70 will induce a circumferential digit magnetic field,H_(D) 90. Since word line 20 is above MRAM device 10, in the plane ofthe element, H_(W) 80 will be applied to MRAM device 10 in the positivey-direction for a positive word current 60. Similarly, since digit line30 is below MRAM device 10, in the plane of the element, H_(D) 90 willbe applied to MRAM device 10 in the positive x-direction for a positivedigit current 70. It will be understood that the definitions forpositive and negative current flow are arbitrary and are defined herefor illustrative purposes. The effect of reversing the current flow isto change the direction of the magnetic field induced within MRAM device10. The behavior of a current induced magnetic field is well known tothose skilled in the art and will not be elaborated upon further here.

[0036] To illustrate how the writing methods for the MRAM array 5 work,it is assumed that a preferred anisotropy axis for magnetic moments 53and 58 is directed at a 45° angle relative to the negative x- andnegative y-directions and at a 450 angle relative to the positive x- andpositive y-directions. As an example, FIG. 2 shows that magnetic moment53 is directed at a 45° angle relative to the negative x- and negativey-directions. Since magnetic moment 58 is generally orientedanti-parallel to magnetic moment 53, it is directed at a 45° anglerelative to the positive x- and positive y-directions. This initialorientation will be used to show examples of the writing methods, aswill be discussed presently.

[0037] Referring to FIG. 4, a graph shows results of a simulatedswitching behavior of the SAF tri-layer structure of bit magnetic region15. The simulation uses two single domain magnetic layers that haveclose to the same moment (a nearly balanced SAF) with an intrinsicanisotropy, are coupled antiferromagnetically, and whose magnetizationdynamics are described by the well known Landau-Lifshitz equation. Thex-axis is the word line magnetic field amplitude in Oersteds, and they-axis is the digit line magnetic field amplitude in Oersteds. Themagnetic fields are applied in a pulse sequence 600 as shown in a timinggraph in FIG. 5. The pulse sequence 600 includes word current 60 anddigit current 70 as functions of time.

[0038] There are three magnetic field regions of operation illustratedin FIG. 4. In a magnetic field region 92 there is no switching. For MRAMoperation in a magnetic field region 95, a direct writing method is ineffect. When using the direct writing method, there is no need todetermine the initial state of the MRAM device because the state is onlyswitched if the state being written is different from the state that isstored. The selection of the written state is determined by thedirection of current in both word line 20 and digit line 30. Forexample, if a ‘1’ is to be written, then the direction of current inboth lines will be positive. If a ‘1’ is already stored in the elementand a ‘1’ is being written, then the final state of the MRAM device willcontinue to be a ‘1’. Further, if a ‘0’ is stored and a ‘1’ is beingwritten with positive currents, then the final state of the MRAM devicewill be a ‘1’. Similar results are obtained when writing a ‘0’ by usingnegative currents in both the word and digit lines. Hence, either statecan be programmed to the desired ‘1 or ‘0’ with the appropriate polarityof current pulses, regardless of its initial state. Throughout thisdisclosure, operation in magnetic field region 95 will be defined-as“direct write mode”.

[0039] For MRAM operation in a magnetic field region 97, a togglewriting method is in effect. When using the toggle writing method, thereis a need to determine the initial state of the MRAM device beforewriting because the state is switched every time the MRAM device iswritten to, regardless of the direction of the currents as long as thesame polarity current pulses are chosen for both word line 20 and digitline 30. For example, if a ‘1’ is initially stored then the state of thedevice will be switched to a ‘0’ after one positive current pulsesequence is flowed through the word and digit lines. Repeating thepositive current pulse sequence on the stored ‘0’ state returns it to a‘1’. Thus, to be able to write the memory element into the desiredstate, the initial state of MRAM device 72 must first be read andcompared to the state to be written. The reading and comparing mayrequire additional logic circuitry, including a buffer for storinginformation and a comparator for comparing memory states. MRAM device 72is then written to only if the stored state and the state to be writtenare different. One of the advantages of this method is that the powerconsumed is lowered because only the differing bits are switched. Anadditional advantage of using the toggle writing method is that onlyuni-polar voltages are required and, consequently, smaller transistorscan be used to drive the MRAM device. Throughout this disclosure,operation in magnetic field region 97 will be defined as “toggle writemode”.

[0040] Both writing methods involve supplying currents in word line 20and digit line 30 such that magnetic moments 53 and 58 can be orientedin one of two preferred directions as discussed previously. To fullyelucidate the two switching modes, specific examples describing the timeevolution of magnetic moments 53, 58, and 40 are now given.

[0041] Referring to FIG. 6, a vector diagram shows the toggle write modefor writing a ‘1’ to a ‘0’ using pulse sequence 600 in MRAM device 72.In this illustration at time to, magnetic moments 53 and 58 are orientedin the preferred directions as shown in FIG. 2. This orientation will bedefined as a ‘1’.

[0042] At a time t₁, a positive word current 60 is turned on, whichinduces H_(W) 80 to be directed in the positive y-direction. The effectof positive H_(W) 80 is to cause the nearly balanced anti-aligned MRAMtri-layer to “flop” and become oriented approximately 90° to the appliedfield direction. The finite antiferromagnetic exchange interactionbetween ferromagnetic layers 45 and 55 will allow magnetic moments 53and 58 to now deflect at a small angle toward the magnetic fielddirection and net magnetic moment 40 will subtend the angle betweenmagnetic moments 53 and 58 and will align with H_(W) 80. Hence, magneticmoment 53 is rotated in clockwise direction 94. Since net magneticmoment 40 is the vector addition of magnetic moments 53 and 58, magneticmoment 58 is also rotated in clockwise direction 94.

[0043] At a time t₂, positive digit current 70 is turned on, whichinduces positive H_(D) 90. Consequently, net magnetic moment 40 is beingsimultaneously directed in the positive y-direction by H_(W) 80 and thepositive x-direction by H_(D) 90, which has the effect of causing netmagnetic moment 40 to further rotate in clockwise direction 94 until itis generally oriented at a 45° angle between the positive x- andpositive y-directions. Consequently, magnetic moments 53 and 58 willalso further rotate in clockwise direction 94.

[0044] At a time t₃, word current 60 is turned off so that now onlyH_(D) 90 is directing net magnetic moment 40, which will now be orientedin the positive x-direction. Both magnetic moments 53 and 58 will nowgenerally be directed at angles passed their anisotropy hard-axisinstability points.

[0045] At a time t₄, digit current 70 is turned off so a magnetic fieldforce is not acting upon net magnetic moment 40. Consequently, magneticmoments 53 and 58 will become oriented in their nearest preferreddirections to minimize the anisotropy energy. In this case, thepreferred direction for magnetic moment 53 is at a 45° angle relative tothe positive y- and positive x-directions. This preferred direction isalso 180° from the initial direction of magnetic moment 53 at time toand is defined as ‘0’. Hence, MRAM device 72 has been switched to a ‘0’.It will be understood that MRAM device 72 could also be switched byrotating magnetic moments 53, 58, and 40 in counter clockwise direction96 by using negative currents in both word line 20 and digit line 30,but is shown otherwise for illustrative purposes.

[0046] Referring to FIG. 7, a vector diagram shows the toggle write modefor writing a ‘0’ to a ‘1’ using pulse sequence 600 in MRAM device 72.Illustrated are the magnetic moments 53 and 58, as well as net magneticmoment 40, at each of the times t₀, t₁, t₂, t₃, and t₄ as describedpreviously showing the ability to switch the state of MRAM device 10from ‘0’ to 1’ with the same current and magnetic field directions.Hence, the state of MRAM device 72 is written to with toggle write mode,which corresponds to magnetic field region 97 in FIG. 4.

[0047] For the direct write mode, it is assumed that magnetic moment 53is larger in magnitude than magnetic moment 58, so that magnetic moment40 points in the same direction as magnetic moment 53, but has a smallermagnitude in zero field. This unbalanced moment allows the dipoleenergy, which tends to align the total moment with the applied field, tobreak the symmetry of the nearly balanced SAF. Hence, switching canoccur only in one direction for a given polarity of current.

[0048] Referring to FIG. 8, a vector diagram shows an example of writinga ‘1’ to a ‘0’, using the direct write mode using pulse sequence 600 inMRAM device 72. Here again, the memory state is initially a ‘1’ withmagnetic moment 53 directed 45° with respect to the negative x- andnegative y-directions and magnetic moment 58 directed 45° with respectto the positive x- and positive y-directions. Following the pulsesequence as described above with positive word current 60 and positivedigit current 70, the writing occurs in a similar manner as the togglewrite mode as described previously. Note that the moments again ‘FLOP’at a time t₁, but the resulting angle is canted from 90° due to theunbalanced moment and anisotropy. After time t₄, MRAM device 10 has beenswitched to the ‘0’ state with net magnetic moment 40 oriented at a 45°angle in the positive x- and positive y-directions as desired. Similarresults are obtained when writing a ‘0’ to a ‘1’ only now with negativeword current 60 and negative digit current 70.

[0049] Referring to FIG. 9, a vector diagram shows the magnetic momentsrotations in MRAM device 72 for an example of writing using the directwrite mode when the new state is the same as the state already stored.In this example, a ‘0’ is already stored in MRAM device 72 and currentpulse sequence 600 is now repeated to store a ‘0’. Magnetic moments 53and 58 attempt to “flop” at a time t₁, but because the unbalancedmagnetic moment must work against the applied magnetic field, therotation is diminished. Hence, there is an additional energy barrier torotate out of the reverse state. At time t₂, the dominant moment 53 isnearly aligned with the positive x-axis and less than 45° from itsinitial anisotropy direction. At a time t₃, the magnetic field isdirected along the positive x-axis. Rather than rotating furtherclockwise, the system now lowers its energy by changing the SAF momentsymmetry with respect to the applied field. The passive moment 58crosses the x-axis and the system stabilizes with the dominant moment 53returned to near its original direction. Therefore, at a time t₄ whenthe magnetic field is removed, and the state stored in MRAM device 72will remain a ‘0’. This sequence illustrates the mechanism of the directwrite mode shown as magnetic field region 95 in FIG. 4. Hence, in thisconvention, to write a ‘0’ requires positive current in both word line20 and digit line 30 and, conversely, to write a ‘1’ negative current isrequired in both word line 20 and digit line 30.

[0050] If larger fields are applied, eventually the energy decreaseassociated with a flop exceeds the additional energy barrier created bythe dipole energy of the unbalanced moment which is preventing a toggleevent. At this point, a toggle event will occur and the switching isdescribed by magnetic field region 97.

[0051] Magnetic field region 95, in which the direct write mode applies,can be expanded, i.e. toggle mode magnetic field region 97 can be movedto higher magnetic fields, if the times t₃ and t₄ are equal or made asclose to equal as possible. In this case, the magnetic field directionstarts at 45° relative to the bit anisotropy axis when word current 60turns on and then moves to parallel with the bit anisotropy axis whendigit current 70 turns on. This example is similar to the typicalmagnetic field application sequence. However, now word current 60 anddigit current 70 turn off substantially simultaneously, so that themagnetic field direction does not rotate any further. Therefore, theapplied field must be large enough so that the net magnetic moment 40has already moved past its hard-axis instability point with both wordcurrent 60 and digit current 70 turned on. A toggle writing mode eventis now less likely to occur, since the magnetic field direction is nowrotated only 45°, instead of 90° as before. An advantage of havingsubstantially coincident fall times, t₃ and t₄, is that now there are noadditional restrictions on the order of the field rise times t₁ and t₂.Thus, the magnetic fields can be turned on in any order or can also besubstantially coincident.

[0052] The writing methods described with reference to FIGS. 4-13,herein called the Savtchenko writing technique, are highly selectivebecause only the MRAM device that has both word current 60 and digitcurrent 70 turned on between time t₂ and time t₃ will switch states.This feature is illustrated in FIGS. 12 and 13. FIG. 10 is a timinggraph that shows a pulse sequence 600 used in MRAM device 72 when wordcurrent 60 is not turned on and digit current 70 is turned on. FIG. 11is a vector diagram that shows the corresponding behavior of the stateof MRAM device 72. At a time to, magnetic moments 53 and 58, as well asnet magnetic moment 40, are oriented as described in FIG. 3. In pulsesequence 600, digit current 70 is turned on at a time t₁. During thistime, H_(D) 90 will cause net magnetic moment 40 to be directed in thepositive x-direction.

[0053] Since word current 60 is never switched on, magnetic moments 53and 58 are never rotated through their anisotropy hard-axis instabilitypoints. As a result, magnetic moments 53 and 58 will reorient themselvesin the nearest preferred direction when digit current 70 is turned offat a time t₃, which in this case is the initial direction at time to.Hence, the state of MRAM device 72 is not switched. It will beunderstood that the same result will occur if word current 60 is turnedon at similar times described above and digit current 70 is not turnedon. Furthermore, it will be understood that even if both the wordcurrent 60 and the digit current 70 are both turned on simultaneously,with non-varying magnitudes, the same result will occur. This featureensures that only one MRAM device in an array will be switched, whilethe other devices will remain in their initial states. As a result,unintentional switching is avoided and the bit error rate is minimized.Thus, in an approach analogous to that used for the MRAM device 71described with reference to FIGS. 2 and 3, there is a region of valuesfor the applied magnetic field within which there is assurance that thebit magnetic moment will not be rotated from one stable polarity toanother in the bit easy axis 59. This region of values corresponds tothe magnetic field region 92 described with reference to FIG. 4,although it will be appreciated that the size of the non-switchingmagnetic field region for an MRAM being commercially distributed will beslightly smaller than the illustrated size of the magnetic field regionas simulated for one device, to account for manufacturing variations.

[0054] One vital performance characteristic of the MRAM device 72 is thepower used to write information into it, and the power is directlyrelated to the field strength required for switching (also called hereinthe “flop field”). It will be appreciated that the strength of anapplied magnetic field required for causing the magnetic material of anearly balanced SAF to flop is determined by the anisotropy of the SAFstructure (bit magnetic region 15) and the saturation field of the SAFstructure (not shown in FIG. 4.) These parameters are, in turn, theresult of engineering decisions that are made during the design of theMRAM device 72 to optimize many aspects of the MRAM fabrication andperformance. For a particular relationship of field components (such asH_(W)=H_(D)), the flop field required to effect a flop of the magneticmoment is conventionally modeled by H_(flop)=sqrt(H_(k) * H_(sat)) whereH_(flop) is the field strength required for switching in the togglemode, H_(k) is the anisotropy, and H_(sat) is the SAF saturation fieldof the structure. However, in accordance with the preferred embodimentof the present invention, small regions dispersed within the MRAM device72 formed during fabrication of the MRAM device 72, called herein“weakly coupled regions” (WCR), overcome the antiferromagnetic couplingpresent in the rest of the sample, saturate, and becomeferromagnetically aligned, in fields much less than H_(sat), Theseregions cause a reduction of H_(flop) by an amount measured in someexperiments to be approximately 50% of that given by the above formula.It will be appreciated that this reduction reduces the power consumptionof an MRAM array considerably and is therefore a very desirable benefit.In addition to having a measurably reduced flop field (when compared tothe conventional model), the WCR are characterized by an extrapolatedmagnetic remanence that is not present in nearly balanced SAF structuresthat are not formed as described herein below.

[0055] Referring to FIG. 12, a graph shows plots of a normalizedmagnetic moment versus a field applied along the magnetic easy axis fortwo samples of nearly balanced synthetic antiferromagnetic structures;one sample fabricated in a conventional manner, herein known as theconventional SAF, and the other fabricated in accordance with thepreferred embodiments of the present invention. These are bulk sampleswherein the SAF is constructed of ferromagnetic layers of NiFe and anantiferromagnetic exchange coupling material of Ru. The anisotropy forthis structure is 5 Oe. Plot 1405 is the plot of the normalized magneticmoment versus an applied field for the sample fabricated in aconventional manner. The low field behavior of plot 1405 is betterviewed in FIG. 13, which is an enlarged view of the center portion ofFIG. 12. It can be seen that as the field is increased from zero field,initially, there is no change in the moment. This corresponds to nochange in the magnetization state for the sample over this field range.When the field reaches 1435, a value of the field for this case ofroughly 35 Oe, there is a sudden change in the net moment from thesample. This corresponds to the SAF flop mentioned previously and thevalue of the field at this point, H_(flop1), is called the flop field.The moments of the two layers are substantially anti-parallel but noworiented 90 degrees to the applied field direction. As the applied fieldincreases further there is a linear region which corresponds to theangle between the moments of the two layers reducing as each momentpoints more and more in the direction of the applied field. When theapplied field reaches a value of applied field, 1425, both moments arepointing in the direction of the applied field and the sample moment issaturated. This value is approximately 255 Oe for this sample. It can beappreciated that these values for Hk (5 Oe), Hsat (255 Oe), and the flopfield, H_(flop1,) (35 Oe) provide good agreement with the modelmentioned above; 35 is approximately equal to sqrt(5*255). Also shown inFIGS. 12 and 13 is an extrapolation of the linear response of momentwith field back to zero field 1415. For a conventional SAF 1405, thevalue of the extrapolation at zero field is zero.

[0056] Plot 1410, shown in FIGS. 12 and 13, is the plot of normalizedmoment versus an applied field for the SAF sample fabricated inaccordance with the preferred embodiments of the present invention. Itis the same sample mentioned above after annealing. Referring now toFIG. 13, it can be seen that plot 1410 has similar behavior in the lowfield portion of the plot where the applied field is near zero. The zerofield behavior of the SAF structure fabricated in accordance with thepreferred embodiments of the present invention is identical to that of aSAF fabricated in the conventional manner; at zero field the sample iscompletely antiferromagnetically coupled. Since reading is performed inzero field, it is highly advantageous to have the zero field behavior ofthe SAF structure fabricated in accordance with the preferredembodiments of the present invention be identical to that of a SAFfabricated in the conventional manner. However, it will be appreciatedthat the value (strength) 1440 of the applied magnetic field at whichthe flop of the magnetic moment occurs, H_(flop2), is nearly one-half(approximately 18 Oersteds) of the flop field 1435 (approximately 35Oersteds), H_(flop1), for the conventionally fabricated SAF sample.Furthermore, for this SAF sample fabricated in accordance with thepreferred embodiment of the present invention, the plot 1410 shows thatthe magnetic moment reaches saturation at an applied field strength1430, H_(sat2), of about 208 Oersteds. Unlike the conventional SAFmentioned above, there is no agreement between these values Hk (5 Oe),Hsat (208 Oe), and the flop field, H_(flop1,) (18 Oe); 18 does not equalsqrt(5*208). The flop field for the sample fabricated in accordance withthe preferred embodiment of the present invention reduces the flop fieldbelow a SAF with a similar anisotropy and SAF saturation thereforereducing the power used to write information.

[0057] Also shown in FIGS. 12 and 13, is an extrapolation 1420 of alinear portion of plot 1410, to approximately 0.12 along the vertical,normalized moment axis when the applied field is zero. This intersectionis called herein the extrapolated remanence. The WCR give rise to theextrapolated remanence exhibited by the sample of nearly balanced (SAF)structure fabricated in accordance with the preferred embodiments of thepresent invention. Not being bound by theory, it is believed that theseweakly coupled regions of the SAF maintain antiparallel alignmentbetween the ferromagnetic layers at zero field thus behaving in asimilar fashion to a conventional SAF. This is most likely due to theexchange coupling between these regions and the surroundingferromagnetic material that still is experiencing a strong antiparallelcoupling. However at a field lower than the conventional flop field theWCR saturate becoming ferromagnetically aligned. This is evidenced bythe larger increase in moment after the flop transition for the SAF withWCR than without. This field at which these WCR saturate correspondswith reduced flop field for the SAF. It is believed that themagnetization change in these WCR induces the reduced flop for theentire sample. The saturation of the WCR is deduced from the identicallinear relationship between moment and applied field for the remaininghysteresis loop between the SAF with and without the WCR. By thistheory, the WCR add moment until the flop is complete (saturate) andsubsequently the remaining regions of the sample that are stillantiferromagnetically coupled exhibit a similar response to fieldthrough to saturation. Extrapolating this linear region back to zerofield provides a way to quantify the amount in moment of the sample thatis contained within these WCR and defines the extrapolated remanencementioned above. For this sample these regions form approximately 12% ofthe total area. A conventional SAF will have an extrapolated remanenceof zero since such a SAF does not possess any of these easily saturatedWCR. Evidence from X-ray diffraction supports the ideas that theseregions are not the result of a significant structural failure of thestructure, but rather a thin point at which the weakened couplingbetween the two ferromagnetic layers can develop. The similar behaviorof the linear region after the flop when comparing a SAF with the WCR toone without the WCR also supports the idea that there is not asignificant change in the majority of the sample; it behaves the same,and supports the theory that the difference resides in the added momentduring the flop. An upper boundary for the percentage of the area of thesample that these regions can form without providing significant realremanence in a SAF, based on the experiments, is approximately 20percent. If the SAF structure were to be annealed at temperatures higherthan those used in accordance with one embodiment of the presentinvention, these regions would grow and remain ferromagnetically coupledeven at zero field. With such high temperature annealing, physicalbridges form between the ferromagnetic layers, overwhelming theantiparallel coupling in the regions surrounding the contact point andcausing real (non-extrapolated) remanence.

[0058] Referring to FIG. 14, a perspective drawing of a portion of theSAF structure 15 is shown after it has been fabricated in accordancewith the present invention. As mentioned above, the dispersed regions1610 are called herein weakly coupled regions (WCR). A SAF structureexhibiting any non-zero extrapolated remanence is a SAF having WCR thathas been formed in accordance with the present invention. Furthermore, aSAF exhibiting a flop field significantly reduced from the valuepredicted from the model presented above is a SAF having WCR that hasbeen formed in accordance with the present invention.

[0059] The dispersed regions 1610 are formed, in accordance with thepreferred embodiment of the present invention, by annealing a nearlybalanced SAF structure that has been fabricated using conventionaldeposition techniques, with the ferromagnetic layers and theantiparallel coupling layer having essentially uniform (but notnecessarily equal) thicknesses. This process does not significantlyalter the nominal thicknesses of the layers 45, 55, 65 of the nearlybalanced SAF. The annealing is performed at a temperature and for aduration that is experimentally determined, for a particular set ofmaterials and size parameters of a SAF structure, to optimize thebenefits of the WCR by reducing the flop field, while avoiding permanentremanence.

[0060] In accordance with another embodiment of the present invention, amethod for forming the WCR is to fabricate the antiparallel couplinglayer as a plurality of layers. The layers may be of differing materialsand may include one or both of antiferromagnetic exchange couplingmaterials and spacing materials, as described above. The layers aredeposited in a manner experimentally determined to optimize the benefitsof the WCR by reducing the flop field while avoiding permanentremanence.

[0061] In accordance with another embodiment of the present invention, avery thin uniform layer of antiferromagnetic exchange coupling materialcan be deposited, followed by another layer of antiferromagneticexchange coupling material that is deposited using a material that isselected for and deposited in a manner that induces thickness variationsthat are experimentally determined to achieve the optimized results. Thematerial and deposition parameters are chosen to optimize the desiredresults.

[0062] In accordance with another embodiment of the present invention,the WCR are formed by co-depositing a spacer material with theantiferromagnetic exchange material such that regions of reducedcoupling are dispersed throughout the sample. This spacer material couldbe immiscible to the exchange layer used, so as to provide largerregions of reduced coupling dispersed throughout the sample. Thematerial and deposition parameters are chosen to optimize the desiredresults.

[0063] In accordance with yet another embodiment of the presentinvention, a method for forming the WCR is by depositing a firstferromagnetic layer, then roughening the surface of the ferromagneticlayer, using any well known technique for doing so—for example, byetching or abrading the layer; then depositing the antiparallel couplinglayer followed by a second ferromagnetic layer. The first ferromagneticlayer may also be treated so as to induce a three dimensionalisland-like growth in the antiferromagnetic coupling layer.

[0064] Memory systems 450, 550 as described herein can be included incomplicated systems-on-a-chip that include, for example an essentiallycomplete cellular radio, or in microprocessors that are used in a verywide variety of electronic devices, including consumer products rangingfrom portable music players to automobiles; military products such ascommunication radios and communication control systems; and commercialequipment ranging from extremely complicated computers to robots tosimple pieces of test equipment, just to name some types and classes ofelectronic equipment.

[0065] Referring now to FIG. 15, a flow chart shows some steps of aprocess for fabricating an SAF structure that can be used in amagnetoresistive tunneling junction memory cell, using the techniquesdescribed in this disclosure. Some steps that have been described hereinabove and some steps that are obvious to one of ordinary skill in theart are not shown in the flow chart, but would be used to fabricate theSAF structure. At step 1710, a first ferromagnetic layer 55 (FIG. 2) isdeposited on a substrate, such as a substrate for a plurality ofintegrated circuits that each include an array of magnetoresistivetunneling junction memory cells that are accessed for reading andwriting by an electronically addressable matrix of conductors, or asubstrate for a memory that is accessed for reading and writing by amoving read/write head, such as a disk drive. The substrate may have hadpatterned layers formed on it before step 1710. At step 1715, anantiparallel coupling layer 65 (FIG. 2) is deposited over the firstferromagnetic layer. A second ferromagnetic layer 45 (FIG. 2) isdeposited, at step 1720, over the antiparallel coupling layer 65, and atstep 1725 WCR 1610 (FIG. 14) are formed in the antiferromagneticexchange coupling layer. The WCR 1610 are formed by annealing, as shownin step 1730, or by depositing the antiparallel coupling layer on thefirst ferromagnetic layer, which has been fabricated to have a roughsurface, as shown in step 1735, or by a multi-layer deposition of theantiparallel coupling layer on the first ferromagnetic layer, as shownin step 1740, or by forming the antiparallel coupling layer as an alloyof a spacer material and an exchange coupling material, for example, byco-depositing the spacer and exchange coupling materials on the firstferromagnetic layer, as shown in step 1745. Forming the WCR by annealingcan occur at any point after the layers are deposited. The WCR can alsobe formed by using combinations of the methods described with referenceto steps The SAF of the magnetoresistive tunneling junction memory cellcan be characterized in several ways that include characterization by avalue of a flop field that is significantly below the square root of theproduct of an anisotropy and SAF saturation of the structure, as shownin block 1830, or characterization by a normalized extrapolatedremanence that is greater than zero, as shown in block 1835.

[0066] It will be appreciated that the unique SAF structure describedherein is advantageous in memory cells with which the Savtchenko writingtechnique is used (memory cells of either the tunneling type ornon-tunneling type), and the SAF structure described herein may beuseful in other magnetoelectronic devices as well, wherein low switchingfields are important.

[0067] In the foregoing specification, the invention and its benefitsand advantages have been described with reference to specificembodiments. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the present invention as set forth in the claims below.Accordingly, the specification and figures are to be regarded in anillustrative rather than a restrictive sense, and all such modificationsare intended to be included within the scope of present invention. Thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims.

[0068] As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

What is claimed is:
 1. A magnetoelectronic memory device that comprises:a nearly balanced synthetic antiferromagnetic (SAF) structure,comprising two ferromagnetic layers, and an antiparallel coupling layerseparating the two ferromagnetic layers and having weakly coupledregions (WCR) therein; and a means for inducing an applied magneticfield in the nearly balanced SAF.
 2. The magnetoelectronic memory deviceaccording to claim 1, wherein the nearly balanced SAF structure is a bitmagnetic region having a bit magnetic moment that has a polarity in abit easy axis when there is no applied magnetic field, furthercomprising: an electrically insulating material designed to form amagnetoresistive tunneling barrier, wherein the bit magnetic region ispositioned on one side of the electrically insulating material; and areference magnetic region positioned on an opposite side of theelectrically insulating material, wherein the electrically insulatingmaterial and the bit and reference magnetic regions form amagnetoresistive tunneling junction device (MTJD).
 3. Themagnetoelectronic memory device according to claim 1, wherein each ofthe two ferromagnetic layers comprises at least one of a group ofelements consisting of Ni, Fe and Co, Mn.
 4. The magnetoelectronicmemory device according to claim 1, wherein the antiparallel couplinglayer comprises al least one of a group of elements consisting of Ru,Os, Re, Cr, Rh, Cu, Nb, Mo, Ta, W, Ir, and V.
 5. The magnetoelectronicmemory device according to claim 1, wherein the antiparallel couplinglayer comprises one of an insulator and a conductor.
 6. Themagnetoelectronic memory device according to claim 1, wherein the nearlybalanced SAF structure has an aspect ratio in a range from 1 to
 5. 7.The magnetoelectronic memory device according to claim 1, wherein thetwo ferromagnetic layers have a moment difference not greater than 15percent.
 8. The magnetoelectronic memory device according to claim 1,wherein the two ferromagnetic layers have a thickness in a range from 5to 150 Angstroms.
 9. The magnetoelectronic memory device according toclaim 1, wherein the antiparallel coupling layer has a nominal thicknessin a range from 3 to 30 Angstroms.
 10. The magnetoelectronic memorydevice according to claim 1, wherein the nearly balanced SAF structurecomprises N ferromagnetic layers (including the two ferromagneticlayers) separated from each other by antiparallel coupling layers, whereN is a whole number greater than or equal to two.
 11. Themagnetoelectronic memory device according to claim 10, wherein at leastone of the antiparallel coupling layers comprises at least one of agroup of elements consisting of Ru, Os, Re, Cr, Rh, Cu, Nb, Mo, Ta, W,Ir, and V.
 12. The magnetoelectronic memory device according to claim10, wherein at least one of the antiparallel coupling layers comprisesone of an insulator and a conductor.
 13. The magnetoelectronic memorydevice according to claim 10, wherein a net moment imbalance of the Nferromagnetic layers does not exceed 15%.
 14. The magnetoelectronicmemory device according to claim 1, wherein the WCR are formed byannealing.
 15. The magnetoelectronic memory device according to claim 1,wherein the WCR are regions within which the two ferromagnetic layersare ferromagnetically coupled to each other.
 16. The magnetoelectronicmemory device e according to claim 1, wherein the WCR comprises an alloyof an exchange coupling material and a spacer material.
 17. Themagnetoelectronic memory device according to claim 1, wherein the WCRare formed by multilayer deposition of the antiparallel coupling layer.18. The magnetoelectronic memory device according to claim 1, wherein anormalized extrapolated remanence of the SAF structure is greater thanzero.
 19. The magnetoelectronic memory device according to claim 1,wherein a value of a flop field is significantly below the square rootof the product of the anisotropy and a saturation of the SAF structure.20. A process for fabricating a nearly balanced SAF structure having abit magnetic region that is a nearly balanced syntheticantiferromagnetic (SAF) structure, comprising: depositing a firstferromagnetic layer; depositing an antiparallel coupling layer over thefirst ferromagnetic layer; depositing a second ferromagnetic layer overthe antiparallel coupling layer; and forming weakly coupled regions(WCR) within the antiparallel coupling layer.
 21. The process forfabricating a nearly balanced SAF structure according to claim 20,wherein the forming achieves a normalized extrapolated remanence that isgreater than zero.
 22. The process for fabricating a nearly balanced SAFstructure according to claim 20, further comprising determining a valueof a flop field, wherein the forming is performed until a value of aflop field is significantly below the square root of the product of theanisotropy of the first and second ferromagnetic layers and an SAFsaturation.
 23. The process for fabricating a nearly balanced SAFstructure according to claim 20, further comprising forming the WCR byannealing the antiparallel coupling layer.
 24. The process forfabricating a nearly balanced SAF structure according to claim 20,wherein the forming further comprises depositing alternate layers ofantiferromagnetic exchange coupling material and spacing material duringthe depositing of the antiparallel coupling layer.
 25. The process forfabricating a nearly balanced SAF structure according to claim 20,further comprising roughening a surface of the first ferromagneticlayer, wherein the forming of the WCR occurs during the depositing ofthe antiparallel coupling layer due to the roughened surface.
 26. Theprocess for fabricating a nearly balanced SAF structure according toclaim 20, wherein depositing the antiparallel coupling layer comprisesdepositing an alloy of an exchange coupling material and a spacermaterial formed during the deposition of the alloy.
 27. The process forfabricating a nearly balanced SAF structure according to claim 20,wherein the forming of the WCR comprises using an elevated temperatureduring the depositing of the antiparallel coupling layer.
 28. Theprocess for fabricating a nearly balanced SAF structure according toclaim 20, wherein depositing the first ferromagnetic layer comprisesdepositing a first material and depositing the second ferromagneticlayer comprises depositing the first material.
 29. The process forfabricating a nearly balanced SAF structure according to claim 20,wherein depositing the first and second ferromagnetic layers eachcomprises depositing at least one of a group of elements consisting ofNi, Fe and Co.
 30. The process for fabricating a magnetoresistivetunneling junction memory cell according to claim 20, wherein depositingthe antiparallel coupling layer comprises depositing at least one of agroup of elements consisting of Ru, Os, Re, Cr, Rh, Cu, Nb, Mo, Ta, W,Ir, and V.
 31. The process for fabricating a nearly balanced SAFstructure according to claim 20, wherein depositing the antiparallelcoupling layer comprises depositing one of an insulator and a conductor.32. The process for fabricating a nearly balanced SAF structureaccording to claim 20, further comprising patterning the bit magneticregion to have an aspect ratio in a range from 1 to
 5. 33. The processfor fabricating a nearly balanced SAF structure according to claim 20,wherein the deposition of the first and second ferromagnetic layers inthe bit magnetic region achieves a net moment difference not greaterthan 15 percent.
 34. The process for fabricating a nearly balanced SAFstructure according to claim 20, wherein the deposition of the first andsecond ferromagnetic layers in the bit magnetic region achieves athickness in a range from 5 to 150 Angstroms.
 35. The process forfabricating a nearly balanced SAF structure according to claim 20,wherein the deposition of the antiparallel coupling layer is performeduntil the antiparallel coupling layer has a nominal thickness in a rangefrom 3 to 30 Angstroms.
 36. The process for fabricating a nearlybalanced SAF structure according to claim 20, further comprisingdepositing additional ferromagnetic layers separated from each other byantiparallel coupling layers.
 37. The process for fabricating a nearlybalanced SAF structure according to claim 36, wherein the depositing ofadditional ferromagnetic layers separated from each other byantiparallel coupling layers comprises depositing the additionalantiparallel coupling layers using at least one of a group of elementsconsisting of Ru, Os, Re, Cr, Rh, Cu, Nb, Mo, Ta, W, Ir, and V.
 38. Theprocess for fabricating a nearly balanced SAF structure according toclaim 36, wherein the depositing of additional ferromagnetic layersseparated from each other by antiparallel coupling layers comprisesdepositing each of the additional antiparallel coupling layers using oneof an insulator and a conductor material.
 39. The process forfabricating a nearly balanced SAF structure according to claim 36,wherein the depositing of additional ferromagnetic layers separated fromeach other by antiparallel coupling layers comprises achieves a netmoment imbalance of the N ferromagnetic layers not exceeding 15%.
 40. Amagnetoelectronic device that comprises: at least one write line; and anearly balanced synthetic antiferromagnetic (SAF) structure, comprising:two ferromagnetic layers an antiparallel coupling layer separating thetwo ferromagnetic layers and having weakly coupled regions (WCR)therein.
 41. A magnetoresistive memory cell that comprises: a nearlybalanced synthetic antiferromagnetic (SAF) structure, comprising: twoferromagnetic layers an antiparallel coupling layer separating the twoferromagnetic layers and having weakly coupled regions (WCR) therein;and a means for inducing an applied magnetic field in the nearlybalanced SAF structure.
 42. The magnetoresistive memory cell accordingto claim 41, wherein the magnetoresistive memory cell is one of aplurality of similarly constructed magnetoresistive memory cells of anintegrated circuit.
 43. The magnetoresistive memory cell according toclaim 41, wherein a net moment difference of magnetic moments in the twoferromagnetic layers is not greater than 15 percent.
 44. Themagnetoresistive memory cell according to claim 41, wherein a normalizedextrapolated remanence of the SAF structure is greater than zero. 45.The magnetoresistive memory cell according to claim 41, wherein a valueof a flop field is significantly below the square root of the product ofan anisotropy and a saturation of the SAF structure.
 46. A syntheticantiferromagnetic (SAF) structure, comprising: two ferromagnetic layers;and an antiparallel coupling layer separating the two ferromagneticlayers and having weakly coupled regions (WCR) therein, wherein a netmoment difference of magnetic moments in the two ferromagnetic layers isnot greater than 15 percent.
 47. The synthetic antiferromagnetic (SAF)structure according to claim 46, wherein a normalized extrapolatedremanence of the SAF structure is greater than zero.
 48. The syntheticantiferromagnetic (SAF) structure according to claim 46, wherein a valueof a flop field is significantly below the square root of the product ofan anisotropy and a saturation of the SAF structure.